galaxy formation and evolution with kband …：与k波段的星系形成和演化…

1、 Searching for massive galaxy progenitors with GMASS (Galaxy Mass Assembly ultradeep Spectroscopic Survey) (a progress report) Andrea Cimatti (INAF-Arcetri) M. Bolzonella (INAF-Bologna), P. Cassata (INAF-Milano), E. Daddi (NOAO), M. Dickinson (NOAO), A. Franceschini (Uni-Padova), C. Halliday (INAF-A

2、rcetri), J. Kurk (MPIA), C. Mancini (Uni-Firenze), M. Mignoli (INAF-Bologna), L. Pozzetti (INAF-Bologna), A. Renzini (INAF-Padova), G. Rodighiero (Uni-Padova), P. Rosati (ESO), G. Zamorani (INAF-Bologna) z 0 0 z 1 1 z 1.5-2z 1-2GMASS? Search for the highest redshift ETGs Identify and study the proge

3、nitors of massive ETGs Stellar mass assembly evolution at 1.5z3GMASS main featuresESO VLT + FORS2 Large Program (145h; PI Cimatti)Target field : 50 arcmin2 in the GOODS-South/HUDF regionSample selection : Spitzer+IRAC, m(4.5m) 1.4 Sample size : N(m1.4)= 390 , 210 in 6 spectroscopic masks Ultradeep s

4、pectroscopy to B=27, I=26, 11h-30h integration Complementary to other surveys (depth, no color selections)100% of data taken in service mode up to 31 December 2005 (80% reduced) Reduced and calibrated data will be publicly available worldwide SpitzerVLTArcetriGMASS target field51 arcmin2 within theG

5、OODS-South fieldcovering a large fraction of the K20 andHubble Ultra Deep Field (UDF) areasWhy 4.5m selection ? Best compromise among IRAC bands (sensitivity, PSF, IQ, blending) “Negative” k-correction (the stellar SED peak enters the 4.5m-band for z1.5) Better sensitivity to stellar mass up to z3 L

6、ess affected by dust extinction than K-band1.6mbumpPreliminary redshift statisticsSmall contamination from objectswith zphot 1.4 and zspec 1.4z(phot) or z(spec)z(spec) (literature + GMASS)z(spec) (GMASS only)Spectroscopic redshift efficiency:red (12h-30h): 70% (not final)blue (11h-15h): 95%Compariso

7、n with DRG selectionSpectraJ. KurkAverage spectrum of first blue mask objectsN=35M. MignoliMulti-band SEDsPhotometric SED fitting with known z(spec)UBVRIz + BViz + JH + JHKs + IRACBolzonella, PozzettiStellar mass estimateszspeczphot Main properties Passive or weakly star-formingOld stars (1-3 Gyr)Ma

8、ssive (log M_stars = 10.9 11.2 Msun, Chabrier IMF)Low levels of specific SFR Early-type morphologyStar-formingLow mass blue systems (log M_stars 10 Msun)Red systems with large mass (log M_stars 11+)and strong star formation (50-100 Msun/yr)Red more because of age than dust extinctionHigh specific st

9、ar formationSolar metallicity from UV photospheric features (Halliday et al.)Strong morphological K-correctionStar formation located mostly in outer regions“Transition” phase leading to an old/massive ETG ?Beyond GMASS Optical blank-fields + extremely K-band faint (KAB SFR1000 M_sun/yrPost-starburst

10、s z6.5 ?Masses: 1011-1012+AGN (Mobasher et al. 2006)Superantennae +Av=3Dusty TorusMid-Infrared colours: the bulk of the sources are consistent with a population of starbursts at z2-3Are we looking at a mixed population ?Short summaryGMASS is designed to investigate the physical mechanisms leadingto the formation and mass assembly of mas